1. Field of the Invention
The present invention relates to a light source apparatus having mode selecting functions for giving priority to the color reproduction of a display image or to brightness according to need, and to an image projection apparatus having the light source apparatus.
2. Description of the Related Art
Known conventional image projection apparatuses include a type in which a white-light source is used to produce light separated into primary colors of red (R), green (G) and blue (B), and another type in which an optical semiconductor, for example, one capable of naturally emitting light of primary colors such as a light-emitting diode (LED), is used.
In the above-described image projection apparatus in which a white-light source is used, lamps such as discharge lamps capable of effectively producing high intensity light are often used. Some of these discharge-type lamps, for example, xenon lamps, are light sources extremely excellent in color rendering properties but limited to certain specific products due to high cost and a large lamp size. In general, an extra-high pressure mercury lamp is mainly used as a white-light source of an image projection apparatus and is now used widely, which is, however, not expected to provide sufficient performance in terms of color rendering properties.
In another type in which a photo diode is used, the LED is still far behind the discharge lamp as a single light source in absolute light intensity, although the LED has been now drastically improved in luminous efficiency. Since the LED does not require color separation and can directly emit primary colors of red, green and blue, it can be effectively used in an image projection apparatus based on a color frame sequential method. Further, the photo diode type is easier to use when switching electrical lighting and adjusting light intensity by electric current and free of harmful substances such as mercury, therefore receiving attention as a next generation light source. It has also caught attention as a light source extremely excellent in color rendering properties particularly due to high color purity.
In order to realize the brightness and color rendering properties required by an image projection apparatus, various types of apparatuses combining discharge lamps with photo diodes such as LEDs to fully utilize these two types of light source have been proposed (refer, for example, to Patent Documents Japanese Published Unexamined Patent Application No. 2000-305040, Japanese Published Unexamined Patent Application No. 2003-255465, Patent No. 3015201, Japanese Published Unexamined Patent Application No. Hei 6-141262, Japanese Published Unexamined Patent Application No. 2002-296680, and Japanese Published Unexamined Patent Application No. 2003-263902).
As one example of the above, the projection-type display apparatus as set forth in Japanese Published Unexamined Patent Application No. 2000-305040 discloses a structure in which light acquired by separating light emitted by a discharge white lamp into primary colors and emitted in light of primary colors by a photo diode are modulated by a display device (spatial modulation element) to project the video light. In addition, a light-emitting diode (LED) high in color purity is used as an optical semiconductor, and the light-emitting diode is used to supplement red color composition, which tends to be insufficient in a discharge lamp, and to improve color rendering properties.
As another example, the projection-type display apparatus as set forth in Japanese Published Unexamined Patent Application No. 2003-255465 discloses a structure in which a laser light source is used in place of a light-emitting diode, in an effort to realize the same object of the projection-type display apparatus as set forth in Japanese Published Unexamined Patent Application No. 2000-305040. This is because a light-emitting diode is in general a plane emission diffusion light source and has a smaller light angle, as with laser light, and proves problematic in providing effective illumination light, whereby the video light is not expected to be sufficiently improved in luminance and efficiency.